A variety of downhole tools may be used within a wellbore in connection with producing or reworking a hydrocarbon bearing subterranean formation. Some downhole tools include wellbore isolation devices that are capable of fluidly sealing axially adjacent sections of the wellbore from one another and maintaining differential pressure between the two sections. Wellbore isolation devices may be actuated to directly contact the wellbore wall, a casing string secured within the wellbore, or a screen or wire mesh positioned within the wellbore.
Typically, a wellbore isolation device will be introduced and/or withdrawn from the well as attached to a conveyance, such as a tubular string, wireline, or slickline, and actuated to help facilitate certain completion and/or workover operations. In some applications, the wellbore isolation device may be pumped into the well, and thereby allowing hydraulic forces to propel the device in or out of the wellbore.
Typical wellbore isolation devices include a body and a sealing element disposed about the body. The wellbore isolation device may be actuated by hydraulic, mechanical, or electric means to cause the sealing element to expand radially outward and into sealing engagement with the inner wall of the wellbore wall, a casing string, or a screen or wire mesh. In such a “set” position, the sealing element substantially prevents migration of fluids across the wellbore isolation device, and thereby fluidly isolates the axially adjacent sections of the wellbore.
It is often desirable to run downhole tools into and out of the well as quickly as possible to reduce required labor time and other operational costs. Due to the effects of “swabbing,” however, wellbore isolation devices are limited in how fast they can be run downhole. Swabbing is a phenomenon where the sealing element inadvertently presets due to flow conditions around the wellbore isolation device. More particularly, when wellbore fluids flow around the sealing element during run-in, the high velocity fluid flow can generate a pressure drop that urges the sealing element radially outward and into engagement with the wellbore wall (or a casing string). When such engagement occurs, further movement of the wellbore isolation device within the wellbore carries or “swabs” fluid with it, which can cause the wellbore isolation device to prematurely actuate and/or otherwise damage or destroy the sealing element. As a result, the run-in speed of a wellbore isolation device is generally limited to slow speeds.
Swabbing can also occur when displacing fluids or flowing fluids around the wellbore isolation device while it is suspended in the wellbore and prior to “setting” the sealing element. Swabbing while displacing fluids can cause the sealing element to prematurely actuate. As a result, the volume of fluid being displaced, or the rate of displacement, will be generally limited.